Originally Posted by ShinyShoe
You don't buy it ready mixed. You may see people referring to "pre-mix" That means the oil is added to the fuel tank before going out. Usually at a ration of 50:1 (1litre of oil added to every 50litres of fuel). You can't buy it premixed. Don't think you can buy motorbike 2 stroke premixed anymore - but even if you can the oil is different. Motorbike engines are air cooled and so run hotter than a boat engine which is water cooled. The oils are different (you need an oil that is classed for TC3W).
A litre of TC3W costs about £10, but if you buy 5litres you can reduce the cost to ~£5/litre. You stick 30litres in a red plastic fuel can and then add 600ml of TC3W... Give it a shake to mix - job done.
More modern 2 strokes don't use pre-mixed fuel. So your fuel tank is 'pure' petrol and there is a reservoir on the engine for the TC3W. The engine adds the right amount of oil, either at a fixed rate or some engine management process.
What you need to know about 2 stroke vs 4 stroke:
2 stroke engines are lighter - so you can sometime put more power on the transom because the engine weighs less
(most) 2 stroke engines are simpler (they still break but usually are simpler to fix
2 stroke engines are noisier (if you are underway that *may* be less of an issue. if you are at tick-over or trying to coach/train people it becomes a challenge.
2 stroke engines are smellier
2 stroke engines tend to leave a bit of an oil slick around them at tick over
2 stroke engines can lie of their sides - probably not relevant here but if you have an aux engine etc thats not on a bracket it needs to be 2S or you get a headache.
2 stroke is less fuel efficient
There is a modern variant on 2 stroke that people either love or hate. It uses fancy modern engine management stuff to manage oil use etc... the general rules don't all apply.
There is a lot of marmite in TC3W ;-)
Thank you for this excellent information ShinyShoe. My knowledge of two strokes harks back to my first motorcycle (197cc Fanny B Falcon) and I eventually got sense and went four stroke with a trumpet 3TA bathtub and a Norton 600 Dominator. I finally settled on adoring the power delivery of a V Twin and had a succession of agricultural Moto Guzzi bikes. I am quite short in height so I looked like an ant on a brick on my Guzzi T3.
The point being that my view (from bikes) is that four stroke engines deliver torque across a wide spread of revs and two stroke required to be kept in the power band to make any progress. Smell and noise was my experience of the old Villiers 2T engine. Any other two stroke engines I have seen up close and personal have been the same. The advantage is they are easier to work on than four stroke engines.
I also happen to like Marmite